sd_get_seats, sd_get_sessions, sd_get_uids — Determine available seats, sessions and logged in users
#include <systemd/sd-login.h>
| int sd_get_seats( | char*** seats ); | 
| int sd_get_sessions( | char*** sessions ); | 
| int sd_get_uids( | char*** sessions ); | 
sd_get_seats() may be used
                to determine all currently available local
                seats. Returns a NULL terminated array of seat
                identifiers. The returned array and all strings it
                references need to be freed with the libc
                free(3)
                call after use. Note that instead of an empty array
                NULL may be returned and should be considered
                equivalent to an empty array.
Similar, sd_get_sessions() may
                be used to determine all current login sessions.
Similar, sd_get_uids() may
                be used to determine all Unix users who currently have login sessions.
On success sd_get_seats(),
                sd_get_sessions() and
                sd_get_uids() return the number
                of entries in the arrays. On failure, these calls
                return a negative errno-style error code.